Coding a sequence of pictures

Abstract

In coding a sequence of pictures (P), a motion vector (MV) is established for a block of pixels (B(*,*;n)) in a current picture (P(n)) to be coded. The motion vector (MV) indicates a block of pixels (B(*,*;n−1)) in a previous picture (P(n−1)) which is similar to the block of pixels (B(*,*;n)) in the current picture (P(n)) to be coded. Data (D) relating to the block of pixels (B(*,*;n)) in the current picture (P(n)), is compressed (CMP). The extent to which the data (D) is compressed depends on a compression parameter (CP). The compression parameter (CP) is controlled on the basis of the motion vector (MV). Accordingly, data relating to a block of pixels representing a moving object can be compressed to a relatively small extent, whereas data relating to a block of pixels representing a stationary object can be compressed to a relatively large extent. This allows a relatively good picture quality at a decoding end.

1 . A method of coding a sequence of pictures (P), the method comprising the steps of: 
 establishing a motion vector (MV) indicating a block of pixels (B(*,*;n−1)) in a previous picture (P(n−1)) which is similar to a block of pixels (B(*,*;n) in a current picture P(n) to be coded; and    compressing data (D) relating to the block of pixels B(*,*;n) in the current picture P(n), the extent to which the data (D) is compressed depending on a compression parameter (CP);    characterized in that the method comprises the step of: 
 controlling the compression parameter (CP) on the basis of the motion vector (MV).  
   
     
     
         2 . A method as claimed in  claim 1 , characterized in that the method comprises the steps of: 
 establishing a motion indication (MI) for the block of pixels (B(*,*;n)) in the current picture P(n) on the basis of the motion vector (MV) belonging to the block of pixels (B(*,*;n) and motion vectors (MV+,MV−) belonging to neighboring blocks of pixels; and    controlling the compression parameter (CP) in dependence on the motion indication (MI).    
     
     
         3 . A method as claimed in  claim 1 , characterized in that it comprises the steps of: 
 calculating an average length (AL) of motion vectors (MV) belonging to a group (GRP) of blocks of pixels; and    maintaining the compression parameter (CP) at a global value (VAL_glob) for compressing data (D) relating to the group (GRP) of blocks of pixels, if the average length (AL) is below a threshold (TH).    
     
     
         4 . A method as claimed in  claim 1 , characterized in that it comprises the step of: 
 controlling the compression parameter (CP) on the basis of the length (L) and the orientation (O) of the motion vector (MV).    
     
     
         5 . A method as claimed in  claim 1 , characterized in that it comprises the steps of: 
 establishing a picture-detail indication (PDI) for the block of pixels B(*,*;n) to be coded; and    controlling the compression parameter (CP) on the basis of the motion vector (MV) and the picture-detail indication (PDI) of the data (D) to be compressed.    
     
     
         6 . A method as claimed in  claim 1 , characterized in that it comprises the steps of: 
 calculating a global value (VAL_glob) for the compression parameter (CP) which is valid for all blocks of pixels in the current picture P(n);    calculating a delta value (VAL_delta) for the compression parameter (CP) on the basis of the motion vector (MV); and    controlling the compression parameter (CP) in dependence on a sum of the global value (VAL_glob) and the delta value (VAL_delta).    
     
     
         7 . A video coder for coding a sequence of pictures (P), the video coder comprising: 
 a motion estimator for establishing a motion vector (MV) indicating a block of pixels (B(*,*;n−1)) in a previous picture (P(n−1)) which is similar to a block of pixels (B(*,*;n) in a current picture P(n) to be coded; and    a data compressor for compressing data (D) relating to the block of pixels B(*,*;n) in the current picture P(n), the extent to which the data (D) is compressed depending on a compression parameter (CP);    characterized in that the video coder comprises: 
 a controller for controlling the compression parameter (CP) on the basis of the motion vector (MV).